The present invention relates to a sensor for measurement of ignition current in an internal combustion engine to monitor combustion, especially in the engine of a motor vehicle. Combustion sensors for monitoring combustion in a cylinder of an internal combustion engine are known, which, in part, also function as a spark plug and have a pin-shaped central electrode and a ground electrode.
Spark plugs are known in which knocking in an internal combustion engine is detected by knock sensors and an appropriate evaluation circuit. These knock sensors can, for example, be located in the housing of the spark plug or can be fitted as pressure pick-up rings in the clamping region of the spark plugs. In all these designs, however, the earth electrode of the spark plug is designed as an extension of the housing. These solutions are very complex and expensive. Furthermore, extraneous signals, such as the rattling of valves, are recorded along with the pressure waves and body-borne waves caused by combustion. Evaluation of the ignition current in these solutions is made more difficult by the fact that with threaded spark plugs, the thermal value of the engine block has a negative and not accurately controllable influence on the shape of the measurement curve.